JPH08330050A - Pulse heat power source - Google Patents

Abstract

PURPOSE: To reduce the vibration of a heater chip and increase the control response speed. CONSTITUTION: Transistors 3a-3d turn on or off the DC voltage obtained by a rectifier circuit 1 and a capacitor 2 to convert it into the AC voltage. This AC voltage is fed to a heater chip 5 via a transformer 4. The temperature of the chip 5 is converted into a voltage by a thermocouple 6, and the voltage Vs corresponding to the set temperature is outputted from a switch 8. A PWM control circuit 9 controls the on/off-time of the transistors 3a-3d based on the voltage Vs and the output voltage Vf of an amplifier 7 so that the temperature of the chip 5 becomes the set temperature. Since the frequency of the current fed to the chip 5 can be increased, the vibration of the chip 5 can be suppressed, and the control response speed can be increased.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pulse heat power supply for supplying a current to a heater chip of a pulse heat type reflow soldering device.

[0002]

2. Description of the Related Art Conventionally, there has been a reflow soldering apparatus for locally heating a joined portion by thermocompression bonding of a lead wire to a thin film substrate or the like, or reflow soldering of an IC lead to a printed circuit board. A pulse heating method is one of the local heating methods used in this reflow soldering apparatus. In the pulse heating method, a joining head called a heater chip is used to pressurize the joined portion, and a large current is passed through this heater chip, and the joined portion (solder in the case of reflow soldering) is generated by the Joule heat generated there. It is melted to obtain a bond.

FIG. 3 is a block diagram of a conventional pulse heat power supply for supplying a current to a heater chip of such a reflow soldering device. Reference numeral 23 is a triac, 24 is a transformer for converting the output of the triac 23 into a low voltage, large current and supplying it to the heater chip 25, 26 is a thermocouple attached to the tip of the heater chip 25, and 27 is a thermocouple 26. A differential amplifier for amplifying the obtained thermoelectromotive force, 28
Is a temperature setting switch for setting the temperature of the heater chip 25, 29 is an adder circuit that takes the difference between the output voltage of the amplifier 27 and the output voltage of the switch 28, and 30 is the triac 2
A phase control circuit for controlling the current flowing through the heater chip 25 by turning on / off the switch 3, 31 is a printed circuit board, 32 is a pattern of the circuit board 31, 33 is solder, and 34 is I.
It is C's lead.

Next, the operation of such a pulse heat power supply will be described. First, when the phase control circuit 30 starts operating and outputs a control signal to the triac 23, the triac 23 is turned on, and an AC voltage (AC100V) from a commercial AC power supply (not shown) is applied to the transformer 24.
Electric current begins to flow in the heater chip 25. As a result, the temperature of the heater chip 25 rises, and the temperature of this chip 25 is converted into a voltage by the thermocouple 26. Next, the adder circuit 29 outputs the output voltage of the amplifier 27 that amplifies the thermoelectromotive force of the thermocouple 26 and the switch 28 corresponding to the set temperature.
Outputs the voltage difference from. Then, the phase control circuit 30
Controls the triac 23 so that the temperature of the heater chip 25 reaches the set temperature based on the output of the adding circuit 29.

FIG. 4 is a waveform diagram of the current (solid line) supplied to the transformer 24, and the shaded portion shows the supplied power.
The phase control circuit 30 keeps the temperature of the heater chip 25 at the set temperature by reducing the current as shown in FIG. 4 as the temperature of the heater chip 25 rises and approaches the set temperature. Thus, the solder 33 melts and the pattern 3
2 and the lead 34 are joined.

As described above, in the conventional pulse heat power supply, the AC voltage from the commercial AC power supply is turned on / off by the triac 23.
Since the phase control for turning off is performed, a large current of, for example, 1000 A having a frequency of the AC voltage (50 Hz or 60 Hz) flows into the heater chip 25, and a power feeding portion to the heater chip 25 (wires after the transformer 24, etc.). ) And the chip 25 vibrate according to Fleming's law. Further, since the response speed of the control is as slow as a half cycle unit of the commercial frequency (10 ms at 50 Hz, 8.33 ms at 60 Hz), the temperature of the heater chip 25 overshoots the set temperature Ts at the start of the control as shown in FIG. Occurs.

[0007]

As described above, in the conventional pulse heat power supply, the temperature of the heater chip is controlled by the phase control of the commercial frequency, so that the power supply section to the heater chip and the chip itself vibrate. There has been a problem that displacement is caused when the joined portion is small. Also,
There is a problem that overshoot occurs in the temperature characteristic of the heater chip. The present invention has been made to solve the above problems, and an object of the present invention is to provide a pulse heat power supply in which vibration of a heater chip or the like is small and a control response speed is fast.

[0008]

A pulse heat power supply of the present invention is a rectifying / smoothing circuit for rectifying an input AC voltage into a DC voltage, and a DC voltage obtained by the rectifying / smoothing circuit is switched to switch the primary side of a transformer. A switching element that turns on / off the current supplied to the heater chip, an amplifier that amplifies the output voltage of the thermocouple attached to the heater chip, and a temperature setting switch that outputs a voltage according to the set temperature of the heater chip,
And a PWM control circuit that controls the time for turning on / off the switching element so that the temperature of the heater chip reaches the set temperature based on the outputs of the amplifier and the temperature setting switch.

[0009]

According to the present invention, the output voltage of the thermocouple is amplified by the amplifier, the voltage according to the set temperature of the heater chip is output from the temperature setting switch, and the temperature of the heater chip is set by the PWM control circuit. The switching element is controlled so that

[0010]

1 is a block diagram of a pulse heat power source showing an embodiment of the present invention, and FIG. 2 is a timing chart diagram for explaining the operation of the pulse heat power source. In FIG. 1, 1 is a rectifier circuit that rectifies an input AC voltage, 2 is a capacitor, 3a to 3d are transistors that are switching elements that switch the DC voltage obtained by the rectifier circuit 1 and the capacitor 2, 4 is a transformer, and 5 is a Heater chip, 6 is a thermocouple, 7 is an amplifier that amplifies the output voltage of the thermocouple 6 and outputs a thermocouple feedback voltage Vf, 8
Is a temperature setting switch that outputs a voltage Vs according to the set temperature of the heater chip 5.

Reference numeral 9 denotes a PWM control circuit, which sets the temperature of the heater chip 5 to the set temperature based on the thermocouple feedback voltage Vf and the voltage Vs from the temperature setting switch 8 to turn on / off the transistors 3a to 3d. Control to be. 11 is an error amplifier that outputs the difference between the feedback voltage Vf and the voltage Vs from the temperature setting switch 8 as the voltage V1, 12 is an oscillator that generates the triangular wave voltage V2, 13 is a comparator that compares the voltage V1 and the triangular wave voltage V2, 14 Is a negation circuit, 15 is a T-type flip-flop, 1
Reference numerals 6 and 17 are NOR circuits. The rectifying circuit 1 and the capacitor 2 form a rectifying / smoothing circuit.

Next, the operation of such a pulse heat power supply will be described. The AC voltage (AC200V) from the commercial AC power supply (not shown) is the three-phase full-wave rectifier circuit 1 as shown in FIG.
Is rectified and smoothed by the capacitor 2. The DC voltage generated by such a rectifying / smoothing circuit is converted into an AC voltage of, for example, 1 kHz by turning on / off transistors 3a to 3d described later, and through a transformer 4 that converts this AC into a low voltage and a large current. It is applied to the heater chip 5. In this way, a current starts flowing through the heater chip 5 as in the example of FIG.

The temperature of the heater chip 5 is converted into a voltage by the thermocouple 6. The output voltage of the thermocouple 6 is amplified by the differential amplifier 7 and input to the PWM control circuit 9 as the thermocouple feedback voltage Vf. Also,
By operating the temperature setting switch 8 for setting the temperature of the heater chip 5, the voltage Vs corresponding to the set temperature is set.
Is input to the circuit 9 from the switch 8.

Next, the error amplifier 11 in the PWM control circuit 9 outputs the difference between the thermocouple feedback voltage Vf and the voltage Vs from the temperature setting switch 8 as the voltage V1.
The oscillator 12 generates a triangular wave voltage V2 of 2 kHz as shown in FIG. 2A, and the comparator 13 generates the triangular wave voltage V2.
And the output voltage V1 of the error amplifier 11 are compared. As a result, the output voltage V3 of the comparator 13 is the voltage V1 (see FIG.
In (a), V1a or V1b becomes "H" level as shown in FIG. 2 (b) in the period of triangular wave voltage V2 or more, and becomes "L" level in the period of V2 or less.

Then, the T-type flip-flop 15 inverts the values of the output terminals Q and Q each time the output voltage V4 (FIG. 2C) of the NOT circuit 14 rises from "L" to "H". Let As a result, the output voltages V5a and V5b of the flip-flop 15 are alternately set to the “H” level as shown in FIGS. 2D and 2E, and the output voltages V6 and V7 of the NOR circuits 16 and 17 are also shown in FIG. ) And (g), the level becomes "H" alternately.

Therefore, the set of the transistors 3a and 3b having the voltage V7 as the base input voltage and the set of the transistors 3c and 3d having the voltage V6 as the base input voltage are alternately turned on, and as a result, the transformer 4 is turned on. The current I flowing to the primary side is an alternating current of 1 kHz as shown in FIG. In FIG. 2 (h), T is a control cycle, and the AC frequency is f (1 / the frequency of the triangular wave voltage V2).
2), T = 1 / 2f.

In such a pulse heat power supply, at the first rise, the temperature of the heater chip 5 is lower than the temperature set by the temperature setting switch 8, and the feedback voltage Vf is considerably smaller than the voltage Vs. The output voltage V1 of the error amplifier 11 has a low value (see FIG. 2).
(V1a in (a)). As a result, the period Ton during which the transistors 3a to 3d are turned on in the cycle T becomes longer,
The off period Toff becomes short, and a large current flows through the heater chip 5.

Next, when the temperature of the heater chip 5 rises due to the supply of such a current, the thermocouple feedback voltage Vf rises and approaches the voltage Vs, so the error amplifier 1
The output voltage V1 of 1 rises like V1b of FIG. Therefore, the output voltage V3 of the comparator 13 has a shorter "L" level period and a longer "H" level period than at the rising time, and the transistors 3a to 3d have the output voltage V3 as shown in FIG. The on period Ton becomes shorter and the off period Toff becomes longer.

In this way, by reducing the current supplied to the heater chip 5 as the temperature of the heater chip 5 rises, the heater chip 5 operates to maintain the temperature set by the temperature setting switch 8.
By the on / off control of the transistors 3a to 3d as described above, it is possible to realize a pulse heat power supply that operates similarly to the example of FIG.

By using a so-called inverter that converts a DC voltage obtained by rectifying and smoothing the commercial AC voltage into an AC of 1 kHz, for example, the frequency of the current flowing through the heater chip 5 can be increased, so that the heater can be used. The period in which the power feeding portion to the chip 5 and the chip 5 itself vibrate becomes short, and the vibration can be suppressed. Further, the control response speed (cycle) can be significantly increased to 0.5 ms when the converted AC frequency is 1 kHz and 0.25 ms when the converted AC frequency is 2 kHz. In this embodiment, the three-phase full-wave rectifier circuit is used as the rectifier circuit 1 because the three-phase AC voltage of 200 V is obtained from the commercial power supply. However, when the single-phase AC voltage of 100 V is used, It goes without saying that a phase full-wave rectifier circuit or the like may be used.

[0021]

According to the present invention, the PWM control circuit controls ON / OFF of the switching element, so that a pulse heat power source similar to the conventional one can be realized which keeps the temperature of the heater chip at the set temperature. Since the frequency of the current passed through the chip can be increased, it is possible to suppress the vibration of the power supply section to the heater chip and the heater chip itself. Further, since the control response speed can be significantly increased as compared with the conventional case, overshoot does not occur in the temperature characteristic of the heater chip.

[Brief description of drawings]

FIG. 1 is a block diagram of a pulse heat power supply showing an embodiment of the present invention.

FIG. 2 is a timing chart diagram for explaining the operation of the pulse heat power supply of FIG.

FIG. 3 is a block diagram of a conventional pulse heat power supply.

FIG. 4 is a waveform diagram of a current supplied to the transformer of FIG.

FIG. 5 is a diagram showing an example of a temperature change of a heater chip.

[Explanation of symbols]

1 ... Rectifier circuit, 2 ... Capacitor, 3a-3d ... Transistor, 4 ... Transformer, 5 ... Heater chip, 6 ... Thermocouple,
7 ... Amplifier, 8 ... Temperature setting switch, 9 ... PWM control circuit, 11 ... Error amplifier, 12 ... Oscillator, 13 ... Comparator,
14 ... Negative circuit, 15 ... Flip-flop, 16, 17
... NOR circuit.

Claims (1)

[Claims] 1. A rectifying / smoothing circuit for rectifying an input AC voltage into a DC voltage in a pulse heating power supply for supplying a current to a heater chip of a pulse heating type reflow soldering device connected to a secondary side of a transformer, and the rectification smoothing circuit. A switching element for switching on / off the current supplied to the primary side of the transformer by switching the DC voltage obtained by the smoothing circuit, an amplifier for amplifying the output voltage of the thermocouple mounted on the heater chip, and a heater chip A temperature setting switch for outputting a voltage according to the set temperature of, and PWM control for controlling the time for turning on / off the switching element so that the temperature of the heater chip becomes the set temperature based on the outputs of the amplifier and the temperature setting switch. A pulse heat power supply having a circuit.